The invention concerns a dynamic mixer for mixing flowable media.
With polymer processing, it is known that the properties of the polymers can be broadly affected by means of supplements. For this, it is normal to mix the supplements with the polymer. As supplements, additives, dyes, stabilizers, lubricants or other polymers can be mixed into the base polymer. It is also possible, however, to mix various supplementary agents, such as dyes, with one another prior to adding them to the polymer. For this, it is normal to use dynamic mixers, by means of which the media are mixed inside of a mixing chamber by means of a mixing shaft.
Mixers of this type are described, for example, in the trade article “High-Efficiency-Dynamic Cavity Mixers for Polymer Processing,” F. Dickmeis, Chemical Fibre International, Vol. 57, 2007, Page 45 ff. There, a mechanical mixer is described as consisting of a multipart housing, in which a mixing chamber having a mixing shaft is disposed. The mixing shaft includes a mixing section extending into the mixing chamber, a bearing section, and a drive section extending out of the housing for coupling to a drive. The bearing section of the mixing shaft is disposed in the housing in a manner to accommodate a radial bearing such as a sliding bearing.
With dynamic mixers of this type there are a number of more or less distinct dead spaces in the transitional region between the bearing section and the drive section of the mixing shaft in the housing, in which build-up of the media that is to be mixed collect. Build-up of this type can be used advantageously for lubricating the bearing section of the mixing shaft, but have, however, the disadvantage that, for example, following a color change, undesired impurities remain inside the mixing chamber.
It is therefore an objective of the invention to provide a dynamic mixer for mixing flowable media, in which the housing is designed without any substantial dead spaces on the circumference of the mixing shaft having a direct connection to the mixing chamber.
This objective may be obtained in accordance with the invention by providing a housing that includes a sealing hole for accommodating the drive section of the mixing shaft, and a bearing hole for supporting the bearing section of the mixing shaft and, for accommodating a sealing means, such that the sealing hole has a greater diameter than the bearing hole.
Advantageous embodiments of the invention are defined by the characteristics and combinations of characteristics described below.
The invention has a particular advantage that there is a minimum of transitional zones in the housing between the bearing section of the mixing shaft and the drive section of the mixing shaft. Thus, the bearing hole for supporting the mixing shaft and the sealing hole for sealing the mixing shaft can be designed to be directly adjacent to one another within the housing, wherein an accommodation of the sealing means as far as the bearing hole is possible as a result of the larger sealing hole.
in a particularly advantageous embodiment of the invention and in order to improve the ease of assembly of the individual components, and at the same time, in order to minimize the transition zones between the bearing hole and the sealing hole, an interstice is incorporated in the housing between the bearing hole and the sealing hole.
According to an advantageous embodiment of the invention, the bearing hole is formed in a separate bearing housing, and the sealing hole is formed in a separate sealing housing, wherein the housing parts are connected to one another by means of an interstice, such that they are pressure-sealed. In this manner, the design and production of the housing parts as well as the holes, adapted to the respective function thereof, is possible.
It has been found that in mixing abrasive media, direct interaction between the sealing means and the medium, which is introduced into the bearing hole for a sliding bearing of the mixing shaft, is to be prevented as much as possible in order to avoid the occurrence of increased wear to the sealing means. In this respect, the invention is preferably implemented in which a supporting ring is associated with the sealing means on the circumference of the mixing shaft, by means of which the sealing means is braced against the bearing hole. And as a result movement of the sealing means is substantially prevented so that the sealing means does not end up in a bearing gap between the housing and the mixing shaft as a result of gap extrusion.
The sealing means is preferably designed as a packing gland, which is associated with a pressure spring. The pressure spring can be attached to the housing by means of a screw adapter, for example, in such a manner that the packing gland is tensioned by means of the pressure spring, thus holding it against the support ring. By this means, on one hand, a uniform friction effect on the circumference of the mixing shaft can be generated, and on the other hand, a high degree of sealing is obtained.
In order to ensure that the mixing shaft can rotate with the greatest degree of uniform frictional behavior within the bearing hole, one embodiment of the invention provides a lubricant hole opening into the bearing hole and connected to one of the inlets associated with the bearing hole. By this means it is possible to feed a medium supplied to the mixer directly to the bearing hole, and thereby the sliding bearing. By means of the pressure difference acting on the mixing chamber it is therefore possible to generate a constant lubricant flow toward the mixing chamber.
Depending on the design of the mixing shaft in the region of the mixing section, it may be desirable if the mixing shaft is guided in the mixing chamber without any substantial axial motion. For this, one embodiment of the invention includes an axial bearing outside of the sealing hole and associated with the drive section of the mixing shaft, which is retained by means of an adapter housing connected to the sealing housing. By this means both internal and external axial forces to the mixing shaft can be accommodated. In addition, by this means motion of the mixing shaft, generated by means of gravity, is also prevented in a vertical assembly.
For this it has been shown that an additional seal with respect to the axial bearing is advantageous for preventing any leaks occurring via the mixing shaft leading outward. Thus, it is provided that on the circumference of the drive section of the mixing shaft, between the axial bearing and the sealing means, a shaft seal and an annular chamber are formed, wherein the annular chamber can be filled with a sealing medium. By this means a full sealing against the exterior is created.
For intensive mixing of the media within the mixing chamber, a groove system is preferably implemented, wherein circumferential grooves on the circumference of the mixing shaft and the housing grooves normally interact. For the design of housing grooves of this sort, one embodiment of the invention includes a mixing chamber formed by means of numerous housing rings, which are retained in the housing in a pressure-sealed manner, and which, together with the mixing section in the mixing shaft, form a groove system within the mixing chamber.
The housing rings are preferably disposed between an outlet housing and the bearing housing, wherein the mixing chamber extends from the bearing housing to the outlet housing.
The inlets for the supplying of the media are preferably formed directly on the bearing housing, such that the outlet is integrated at the end of the mixing chamber at the outlet housing.
The dynamic mixer according to the invention is preferably used for the processing of polymers. There is also the possibility that a polymer and a supplementary substance, or only supplementary substances, such as liquid dyes, for example, are mixed.